Objective: To evaluate nutrition-related risk factors for breast and colorectal cancer incidence and mortality. Background: The Breast Cancer Detection and Demonstration Project (BCDDP) has three distinct phases: screening, initial followup, and the current continued followup. Between 1973-1975, approximately 280,000 women aged 35-74 years were recruited from 29 centers throughout the United States to undergo annual breast cancer detection screening examinations which included a physical examination and mammography. After screening was completed in 1979, 64,185 of these women were selected for an additional five years of followup to assess the biology and natural history of breast disease. Methods: A new questionnaire, with new questions on nutrition, physical activity, and body size, was mailed to 60,079 living members of the BCDDP cohort in 1987 through 1989. The new questions, coupled with the collection of endpoint data in 1993-95, has generated a new, large prospective cohort for analyses of diet, nutrition and subsequent breast and colorectal cancer. Progress: A new questionnaire was sent to 58,400 living cohort members in 1993-95. This instrument, in addition to assessing endpoints since 1987-89, included questions on family and reproductive history (updated), exogenous estrogen use (including newer preparations with progestins), breast procedures and mammography, history of cancer and other medical conditions (including history of elevated blood pressure and cholesterol and treatment for such conditions), eating habits (e.g., type of ground meat eaten, whether skin was removed from poultry), adolescent diet, high school/college athletics, disability, body fat distribution, and medication history. It is estimated that approximately 1,100 breast, 300 colorectal, 250 endometrial, and 150 ovarian cancers will be ascertained for the followup period between 1987-89 and 1993-5. Analyses of nutritional and hormonal factors in relation to breast and colorectal cancer are under way.